FR2895522A1 - Transparent substrate for solar module has antireflecting cover presenting selectivity between visible wavelength field including near infrared and wavelength field including far infrared and comprising stack of high and low index layers - Google Patents

Abstract

The substrate has, on a face, an anti-reflecting cover presenting a selectivity between visible a wavelength field including near infrared and a wavelength field including far infrared. The cover comprises a stack of alternative high index layers (1, 3) with refractive indices between 1.85-2.15, and low index layers (2, 4) with refractive indices between 1.35-1.55. The layers (1-4) present thickness between 10-30 nanometers, 20-40 nanometers, 1400160 nanometers and 95-120 nanometers, respectively.

Description

TRANSPARENT SUBSTRATE HAVING ANTIREFLECTION COATING 5

  The invention relates to the use of a transparent substrate, in particular glass, provided on at least one of its faces with an antireflection coating. Antireflection coatings are usually made up, for the simplest, of a thin interferential layer whose refractive index is between that of the substrate and that of air, or, for the most complex, of a stack of thin layers. (In general, alternating layers based on dielectric material with high and low refractive indices). In their most conventional applications, they are used to reduce the light reflection of the substrates, to increase the light transmission. This is for example glazing intended to protect paintings, to make counters or shop windows. Their optimization is therefore taking into account only the wavelengths in the visible range. However, it has been found that it may be necessary to increase the transmission of transparent substrates, and not only in the visible range, for particular applications. These include solar cells (also called solar modules or collectors), for example silicon cells. These cells need to absorb the maximum of the solar energy they capture, in the visible, but also beyond, especially in the near infrared to maximize their quantum efficiency that characterizes their energy conversion efficiency. It has therefore appeared, in order to increase their efficiency, to optimize the transmission of solar energy through this glass in the wavelengths which are important for solar cells. A first solution was to use extra-clear glasses with very low iron oxide (s) content. These are, for example, glasses marketed in the DIAMANT range or in the ALBARINO range by Saint-Gobain Glass France. A second solution was to provide the glass, on the outside, with an antireflection coating consisting of a porous silicon oxide monolayer, the porosity of the material making it possible to lower the refractive index. However, this one-layer coating is not very efficient. It also has a durability, particularly vis-à-vis moisture, insufficient.

  A third solution was to provide the glass, on the outside, with an antireflection coating, especially at least in the visible and in the near infrared, made of a stack (A) of thin layers of refractive index dielectric material. alternatively strong and weak, this antireflection coating has in addition to optimum optical performance in terms of increased light transmission, correct performance in terms of mechanical and chemical durability. Although this third already provides a significant solution in terms of performance of energy conversion efficiency of the solar cell, the inventors have developed a new antireflection coating that is able to further increase the energy conversion efficiency of the solar cell. . The invention firstly relates to the use of a transparent substrate, in particular glass, comprising on at least one of its faces an antireflection coating (A) of dielectric material and which has a selectivity between the range of lengths of d visible wave including near-infrared and wavelength range including far-infrared. Thanks to this selectivity of the antireflection coating, it is possible to lower the operating temperature by a few degrees at the solar cell, and this decrease of a few degrees results in an increase in the conversion efficiency.

  In preferred embodiments of the invention, one or more of the following provisions may also be used: - use of a transparent substrate, in particular glass, comprising on at least one of its faces an antireflection coating (A) of dielectric material and whose selectivity allows a variation of the electrical parameters of the cell (Ise, Voe), -use of an anti-reflection coating made of a stack (A) of thin layers in dielectric material of alternately strong and weak refractive indexes, the stack comprising successively: a first high-index refractive index layer of between 1.85 and 2.15 and of a geometrical thickness and between 10 and 30 nm, a second low-index layer with a refractive index n2 of between 1.35 and 1.55 and a geometric thickness e2 between 20 and 40 nm; a third layer; , high index, index of e refraction n3 between 1.85 and 2.15 and geometric thickness e3 between 140 nm and 160 nm, - a fourth layer, with a low index, with a refractive index n4 of between 1.35 and 1, 55 and geometric thickness e4 between 95 nm and 120 nm. the first high-index layer and / or the third high-index layer are based on metal oxide (s) chosen from zinc oxide, tin oxide, oxide, of zirconium or the mixed oxide of zinc and tin, or based on nitride (s) selected (s) from silicon nitride and / or aluminum nitride, - the first high-index layer and / or the third high-index layer consist of a superposition of several high-index layers, in particular a superposition of two layers such as SnO2 / Si3N4 or Si3N4 / SnO2. the second low-index layer and / or the fourth low-index layer are based on silicon oxide, oxynitride and / or silicon oxycarbide or on a mixed oxide of silicon and aluminum. said substrate is made of glass, clear or extra-clear, textured, and preferably tempered. the stack (A) comprises the following sequence of layers: SnO2 or Si3N4 / SiO2 / SnO2 or Si3N4 / SiO2 or SiAIO - the substrate has an integrated transmission over a wavelength range of between 400 and 1100 nm at least 90%. it also relates to the use of the substrate as previously defined as transparent outer substrate of solar modules comprising a plurality of Si or CIS type solar cells.

  According to another aspect of the invention, it also relates to a solar module comprising a plurality of solar cells of Si, CIS, CdTe, a-Si, GaAs or GalnP type, which uses a substrate as previously defined. According to one embodiment of the solar module it has an increase in its efficiency, expressed in integrated current density, of at least 1, 1.5 or 2% compared to a module using an external substrate without the antireflection stack (A). According to yet another embodiment of the solar module, it comprises two glass substrates, the solar cells being arranged in the inter-glass in which a curable polymer has been cast. Within the meaning of the invention, "layer" is understood to be either a single layer or a superposition of layers where each of them respects the indicated refractive index and the sum of their geometrical thicknesses also remains the value indicated for the layer in question.

  Within the meaning of the invention, the layers are made of dielectric material, in particular of the oxide or nitride type, as will be detailed later. However, it is not excluded that at least one of them is modified so as to be at least a little conductive, for example by doping a metal oxide, this for example to possibly give the antireflection stack also a anti-static function. The invention is preferably concerned with substrates with a glass function, but can also be applied to transparent substrates based on polymer, for example polycarbonate or PC or poly (methyl methacrylate) or PMMA. The invention therefore relates to a four-layer type antireflection stack. This is a good compromise because the number of layers is large enough that their interferential interaction can achieve an important antireflection effect. However, this number remains reasonable enough to be able to manufacture the product on a large scale, on an industrial line, on large substrates, for example by using a vacuum deposition technique of the sputtering type (magnetic field assisted). . The criteria of thickness and refractive index retained in the invention make it possible to obtain a broadband antireflection effect, with a substantial increase in the transmission of the substrate-carrier, not only in the visible range but also in the beyond, especially in the infrared and more particularly in the near infrared. It is a powerful antireflection over a range of wavelengths extending at least between 400 and 1100 nm. The inventors have discovered that the use of a selective antireflection stack makes it possible to combine: in the field covering the wavelengths of the visible and up to those of the near infra-red (typically from 300 to 1300 nm for a cell based on CIS) to obtain a high light transmission which guarantees a high energy conversion efficiency, this high transmission being reflected at the level of the cell by a variation of a characteristic parameter (ISc for Intensity Short Circuit) which precisely conditions this conversion efficiency - in the field from the near infrared to the far infrared (typically 1300 nm to 50000 nm for a CIS-based cell) to obtain a significant reflection of the incident radiation in these lengths. wave, which promotes a significant decrease in the operating temperature of the cell, and which leads at the level of the cell to a variation of a second characteristic parameter The inventors have thus selected thicknesses for the layers of the stack different from the thicknesses usually chosen for conventional antireflection coatings intended to reduce the reflection only in the visible. In the present invention, this selection has been made so as to anti-reflect the substrate not only in the visible but also in the infra-red. The most suitable materials for constituting the first and / or the third layer, those with a high index, are based on metal oxide (s) chosen from zinc oxide ZnO, SnO2i tin zirconium oxide ZrO2. It may especially be a mixed oxide of Zn and Sn, zinc stannate type. They may also be based on nitride (s) chosen from silicon nitride Si3N4 and / or aluminum nitride AlN. Using a nitride layer for one or other of the high index layers, in particular the third at least, makes it possible to add a feature to the stack, namely an ability to better withstand heat treatments without any noticeable deterioration of its optical properties. However, this is a feature that is important for the glasses that must be part of solar cells, because these glasses must generally undergo a heat treatment at high temperature, type quenching, where the glasses must be heated between 500 and 700 C. It then becomes advantageous to be able to deposit the thin layers before the heat treatment without this being a problem, because it is easier industrially to make the deposits before any heat treatment. It is thus possible to have a single antireflection stack configuration, whether or not the carrier glass is intended to undergo heat treatment. Although it is not intended to be heated, it remains interesting to use at least one nitride layer, as it improves the mechanical and chemical durability of the stack as a whole. This is all the more important in applications to solar cells, constantly exposed to climatic hazards. According to a particular embodiment, the first and / or the third layer, those with high index, may in fact consist of several superimposed layers superimposed. It may especially be a bilayer type SnO2 / Si3N4 or Si3N4 / SnO2. The advantage is as follows: Si3N4 tends to be deposited a little less easily, a little slower than a conventional metal oxide such as SnO2i ZnO or ZrO2 by reactive sputtering. For the third layer in particular, which is the thickest and most important to protect the stack from possible damage resulting from heat treatment, it may be interesting to split the layer so as to just the sufficient thickness of Si3N4 to obtain the protective effect vis-à-vis the desired heat treatments, and to "supplement" optically the layer with SnO2i ZnO or a mixed zinc oxide and tin zinc stannate type. The most suitable materials for constituting the second and / or the fourth layer, those with low index, are based on silicon oxide, oxynitride and / or silicon oxycarbide or based on a mixed oxide silicon and aluminum. Such a mixed oxide tends to have a better durability, especially chemical, than pure SiO 2 (an example is given in patent EP-791 562). The respective proportion of the two oxides can be adjusted to achieve the expected improvement in durability without greatly increasing the refractive index of the layer. The glass chosen for the substrate coated with the stack according to the invention or for the other substrates associated with it to form a glazing, may be particular, for example extra-clear of the "diamond" type (low in particular iron oxides). ), or be a standard clear-soda-lime glass of the "Planilux" type, or an extra clear glass of which at least one of the faces has a surface texturing of the Albarino type (three types of glass sold by Saint-Laurent). Gobain Glazing). Particularly interesting examples of the coatings according to the invention comprise the following sequences of layers: for a stack with four layers: SnO 2 or Si 3 N 4 / SiO 2 / SnO 2 or Si 3 N 4 / SiO 2 or SiAlO (SiAlO here corresponds to a mixed oxide of aluminum and of silicon, without prejudging their respective amounts in the material) The substrates of glass type, especially extra-clear, having this type of stack can thus achieve integrated transmission values between 400 and 1300 nm of at least 90%, especially for thicknesses between 2 mm and 8 mm. The subject of the invention is also the substrates coated according to the invention as external substrates for Si or CIS type solar cells.

  This type of product is generally marketed in the form of solar cells mounted in series and arranged between two transparent rigid substrates of the glass type. The cells are held between the substrates by a polymeric (or more) material. According to a preferred embodiment of the invnetion which is described in patent EP 0739 042, the solar cells can be placed between the two substrates, then the hollow space between the substrates is filled with a cast polymer capable of hardening, while particularly polyurethane based on the reaction of an aliphatic isocyanate prepolymer and a polyether polyol. The polymer may be hardened at 30 to 50 ° C. and possibly at a slight overpressure, for example in an autoclave. Other polymers can be used, such as EVA ethylene vinyl acetate, and other mountings are possible (for example, laminating between the two cell glasses using one or more sheets of thermoplastic polymer) . It is the set of substrates, polymer and solar cells that are designated and sold under the name of solar module. The invention therefore also relates to said modules. With the modified substrate according to the invention, the solar modules can increase their efficiency by at least 1, 1.5 or 2% (expressed in integrated current density) with respect to modules using the same substrate but without the coating. When we know that the solar modules are not sold per square meter, but the electric power delivered (approximately, we can estimate that a square meter of solar cell can provide about 130 Watt), each percent of additional yield increases the performance electric, and therefore the price, of a solar module of given dimensions.

  One method of manufacturing the antireflection stack may consist of depositing all the layers, successively, by a vacuum technique, in particular by magnetic field assisted sputtering or corona discharge. Thus, the oxide layers can be deposited by reactive sputtering of the metal in question in the presence of oxygen and the nitride layers in the presence of nitrogen. To make SiO2 or Si3N4, we can start from a silicon target that is slightly doped with a metal such as aluminum to make it sufficiently conductive.

  It is also possible, as advocated by the patent WO97 / 43224, that a part of the layers of the stack is deposited by a hot deposition technique of the CVD type, the remainder of the stack being deposited cold by cathodic sputtering. . The details and advantageous characteristics of the invention will now be apparent from the following nonlimiting examples, with the aid of the figures: FIG. 1 illustrates a substrate provided with a four-layer antireflection stack A according to the invention, FIG. 2 illustrates graphs representing the transmission spectrum of different substrates bare or coated with antireflection stacks according to the various examples of the invention. FIG. 3 illustrates graphs showing the energy gain that can be obtained as a result of a temperature variation, for different types of cells equipped with different substrates. FIG. 4 illustrates a solar module integrating the substrate according to FIG. 1. FIG. 1, very schematic, shows in section a glass 6 surmounted by a four-layer antireflection stack (A) 1, 2, 3, 4. EXAMPLE 1 Example 1 relates to an extra-clear textured glass of the Albarino range which is bare, i.e., it is not coated with any stack. Optical measurements have made it possible to determine a T1 of 91.47% and a solar factor of 91.27%. For this substrate, its selectivity is given below: J • 1300 DOL) xT (a,) d ~, J300 T-efff1300 DO 300 ~~~

  10 and S = Tff TE With: D (X): solar emission spectrum T (X): spectral transmission of glass TE: energy transmission of glass (300-2500nm) After calculation, we obtain S = 1.00

EXAMPLE 2

  Example 2 relates to an extra-clear textured glass of the range

  Albarino coated with an anti-reflective coating based on porous silica. Optical measurements made it possible to determine a T1 of 95.65% and a

  solar factor of 94.01% For this substrate and this antireflection stack, its selectivity S (calculated from the same equations as above) is given below. After calculation, S = 1.02 is obtained.

EXAMPLE 3

  Example 3 relates to an extra-clear textured glass of the Albarino range coated with a four-layer anti-reflective coating.

  Optical measurements made it possible to determine a T1 of 94.60% and a solar factor of 91.35%

  For this substrate and this anti-reflection stack, its selectivity S (calculated from the same equations as above) is given below. After calculation, S = 1.04 is obtained.

  In this example, the antireflection stack used is as follows: Refractive index Example 3 (nm) Si3N4 (1) 1.95 - 2.05 19 SiO2 (2) 1, 47 29 Si3N4 (3) 1.95 - 2 , SiO 2 (4) 1.47 100 25 (Si3N4 can be replaced, for layer (1) and / or for layer (3), with SnO2). The coated glass of Example 3 is mounted as an outer glass of solar modules. FIG. 4 very schematically represents a solar module 10 according to the invention. The module 10 is constituted as follows: the glass 6 provided with the antireflection coating (A) is associated with a glass 8, said inner glass. This glass 8 is made of tempered glass, 4 mm thick, and light extra-clear type (Planidur DIAMANT). The solar cells 9 are placed between the two glasses, then a polyurethane-based curable polymer 7 is poured into the interlayer in accordance with the teaching of patent EP 0 739 042 mentioned above. Each solar cell 9 is constituted, in a known manner, from silicon wafers forming a p / n junction and printed front and rear electrical contacts. Silicon solar cells can be replaced by solar cells using other semiconductors (such as CIS, CdTe, a-Si, GaAs, GalnP). For this solar module, it is also possible to calculate the selectivity integrating the cell (in our case a solar cell based on CIS). ## EQU1 ## xT (X) xReellule (X) dX Tell f 1300 D (X) x R eellule (X,) dX J300 With: D (X): solar emission spectrum T (X): spectral transmission of glass Rceuule (2): response of the photovoltaic cell to a wavelength Selectivity: S = T ## EQU1 ## where: Teff defined above D (X): solar emission spectrum T (X): transmission spectral D '(X): emission spectrum of Abs glass (X): absorption of the photovoltaic cell For simplification of the measurements, we can take: S = T rr TEx (1ùR'E) With: TE: energy transmission of glass (300-2500nm) R'E: energy reflection of the photovoltaic cell (300-2500 nm) For comparison, we mounted a solar module identical to the previous one, but with an outer glass 6 made of extra-clear glass not the rev antireflection ment according to the invention (e.g. that of Example 1).

  FIG. 2 shows, for each of the examples 1, 2, 3, the evolution of the transmission spectrum for wavelengths covering the solar spectrum. This figure 2 also shows the evolution of the quantum efficiency of a cell. This quantum efficiency, for a given cell technology (CIS in this example) makes it possible to quantify the energy conversion efficiency of the cell which is subjected to solar radiation. The selective nature of such an antireflection stack (Example 3) compared to the same bare substrate makes it possible to reduce the increase in the temperature of the cell. FIG. 3 shows the evolution of the temperature of the substrate of Example 1 and of Example 3 over time, when this substrate is subjected to an illumination of a spectrum of wavelengths covering the solar spectrum. As can be seen the substrate of Example 1 (which is a bare glass) heats substantially more than the same substrate of Example 3 which has an antireflection coating. When we study Figure 3, which shows the evolution of the no-load voltage (Voc) for the same substrates of Example 1 and Example 3, we note that this gain is of the order of 1 % (even 2% in some configuartions), which is far from negligible in solar cell technology. GB2 2005127 EN

Claims (13)

  1. Use of a transparent substrate, in particular glass, comprising on at least one of its faces an antireflection coating (A) made of dielectric material and which has a selectivity between the visible wavelength range including the near infrared and the wavelength domain including far infrared.   2. Use of a substrate according to claim 1, characterized in that the selectivity allows a variation of the electrical parameters (Isc, Vos) of a solar cell (9).   3. Use of a substrate according to one of claims 1 or 2, characterized in that the anti-reflection coating comprises a stack (A) of thin layers of dielectric material of refractive index alternately strong and weak, the stack comprising successively: a high-index first layer (1) having a refractive index n1 of between 1.85 and 2.15 and a geometrical thickness e of between 10 and 30 nm; layer (2), with a low index, with a refractive index n2 between 1.35 and 1.55 and a geometric thickness e2 of between 20 and 40 nm, a third layer (3) with a high index, with a refractive index n3 of between 1.85 and 2.15 and a geometric thickness e3 of between 140 nm and 160 nm; a fourth layer (4) with a low index of refractive index n4 of between 1 and , 35 and 1.55 and geometric thickness e4 between 95 nm and 120 nm.   4. Use of a substrate according to claim 3, characterized in that the first high-index layer (1) and / or the third high-index layer (3) are based on metal oxide (s) selected from zinc oxide, tin oxide, zirconium oxide or mixed zinc and tin oxide, or nitride oxide (s) selected from among silicon nitride and / or aluminum nitride.   5. Use of a substrate according to claim 3, characterized in that the first high-index layer (1) and / or the third high-index layer (3) consist of a superposition of several high-index layers, GB2 2005127 EN 2895522 / '14 including a superposition of two layers such as SnO2 / Si3N4 or Si3N4 / SnO2.   6. Use of a substrate according to claim 3, characterized in that the second low index layer (2) and / or the fourth low index layer (4) are based on silicon oxide, oxynitride and / or oxycarbide of silicon or a mixed oxide of silicon and aluminum.   7. Use of a substrate according to one of claims 3 to 6, characterized in that the substrate is glass, clear or extra-clear, textured, and preferably tempered.   8. Use of a substrate according to one of the preceding claims, characterized in that the stack (A) comprises the following sequence of layers: SnO2 or Si3N4 / SiO2 / SnO2 or Si3N4 / SiO2 or SiAIO.   9. Use of a substrate according to one of the preceding claims, characterized in that the substrate has an integrated transmission over a wavelength range of between 400 and 1100 nm of at least 90%.   10. Use of the substrate (6) according to one of the preceding claims, as a transparent outer substrate of solar modules (10) comprising a plurality of solar cells (9) of Si or CIS type.   11. Solar module (10) comprising a plurality of solar cells (9) of the Si, CIS, CdTe, a-Si, GaAs or GalnP type, characterized in that it uses as substrate the substrate (6) according to one of claims 1 to 10.   12. Solar module (10) according to claim 11, characterized in that it has an increase in its efficiency, expressed in integrated current density, of at least 1, or even 2% compared to a module using a substrate. outside 25 without antireflection stack (A).   13. Solar module (10) according to one of claims 11 or 12 characterized in that it comprises two glass substrates (6, 8), the solar cells (9) being arranged in the inter-glass in which one cast a curable polymer (7).